The present invention generally relates to semiconductor processing, and in particular to a system for uniform development of a photoresist material layer on a wafer.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down device dimensions (e.g., at submicron levels) on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller features sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as corners and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon structure, is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, x-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image maybe either a negative or a positive image of the subject pattern. Exposure of the coating through a photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Due to the extremely fine patterns which are exposed on the photoresist material, thickness uniformity of the photoresist material is a significant factor in achieving desired critical dimensions. The photoresist material should be applied such that a uniform thickness is maintained in order to ensure uniformity and quality of the photoresist material layer. The photoresist material layer thickness typically is in the range of 0.1 to 3.0 microns. Good resist thickness control is highly desired, and typically variances in thickness should be less than xc2x110-20 xc3x85 across the wafer. Very slight variations in the photoresist material thickness may greatly affect the end result after the photoresist material is exposed by radiation and the exposed portions removed.
Application of the resist onto the wafer is typically accomplished by using a spin coater. The spin coater is essentially a vacuum chuck rotated by a motor. The wafer is vacuum held onto the spin chuck. Typically, a nozzle supplies a predetermined amount of resist to a center area of the wafer. The wafer is then accelerated to and rotated at a certain speed, and centrifugal forces exerted on the resist cause the resist to disperse over the whole surface of the wafer. The resist thickness obtained from a spin coating process is dependent on the viscosity of the resist material, spin speed, the temperature of the resist and temperature of the wafer.
After the resist is spin coated and selectively irradiated to define a predetermined pattern, the irradiated or unirradiated portions are removed by applying a developer. The developer is also spin coated onto the wafer by applying developer across the resist and then spin coating the developer until centrifugal forces disperse the developer over the coating of resist. However, the developer is not always uniformly dispersed on the wafer because the of the difference of the surface area on the outer peripheral portion of the wafer in comparison to the center portion of the wafer. This may cause overdeveloping of the center portion of the resist on the wafer forming a developed resist layer with a thickness that is smaller at the center than at the outer peripheral surfaces. The result is the predetermined photoresist pattern cannot be formed.
The above stated problems even occur for nozzles that are designed to dispense developer more uniformly, such as a multiple tip dispensing nozzles. Typically, a multiple tip dispensing nozzle includes a chamber for receiving developer that distributes developer to a plurality of nozzles distributed over the length of the nozzle, which extends the diameter of the wafer. FIGS. 1a and 1b illustrate typical problems that can occur in applying developer to a resist on a wafer with a multiple tip nozzle. A multiple tip nozzle 10 is coupled to a pivotable arm 12 that pivots from a rest position 11 to an operating position 15. In the operating position 15, the multiple tip nozzle applies a developer 30 on a resist layer 24 disposed on a wafer 22. The wafer 22 is vacuum held onto a rotating chuck 20 driven by a shaft 26 coupled to a motor 28. The wafer 22 with its coating of resist 24 is rotated at a constant speed and developer 30 is applied through a plurality of tips 14 along a central axis through of the resist layer 24. The tips 14 are aligned at different points along the central axis to apply developer along different annular rings (not shown). The developer 30 flows outward from each annular ring covering the entire top surface of the resist layer 24. FIG. 1a illustrates an example of the problems that can occur after the developer with the irradiated resin portions are spun off the wafer and/or rinsed off the wafer. The center portion of the resist is exposed to more developer due to puddling in the center region of the wafer. As a result, a groove 18 is formed in the central region of the resist resulting in a non-uniformly exposed wafer.
FIG. 1c illustrates a proposed solution for the above described problem. The nozzle 10 is offset from the central axis of the resin 24, so that puddling does not occur in the center of the resist layer 24. This solves the problem with puddling in the central region of the resist layer 24, but due to offset portion lagtime, one side of the wafer receives more developer than the other. FIG. 1d illustrates that the exposed resist layer 24 includes a first surface 34 that is more exposed than a second surface 32 causing a difference in the thickness of the resist 24 along the first and second surface. Again, this undesireability causes a non-uniformly exposed wafer.
The resulting developed resist layers illustrated in FIGS. 1b and 1d do not have uniform thicknesses which may lead to impaired device performance. In view of the above, a system/method is needed, for dispensing a uniform layer of developer across a resist formed on a wafer.
The present invention provides for a system and method that facilitates the application of a uniform layer of developer on a photoresist material layer. The present invention accomplishes this end by utilizing a developer application system that includes a multiple tip nozzle and a movement system that moves the nozzle to a first position offset a predetermined distance from a central axis of a photoresist material layer, and applies a predetermined volume of developer at this first position. The system then moves the nozzle to a second position offset from the same central axis a predetermined distance at the opposite side of the central axis with respect to the first axis, and applies a predetermined volume of developer at this second position, such that the longitudinal axis of the nozzle in the first and the second position is parallel to the central axis. The predetermined positions, distances and volumes are those positions, distances and volumes that allow for forming a uniformly thick layer of developer on the photoresist material layer that provides for a uniformly thick layer of developed photoresist material layer. These values are typically chosen based on historical data for the particular process being performed.
The present invention also provides a measurement system that measures the thickness uniformity of the developed photoresist material layer disposed on a test wafer. In one aspect of the invention, the thickness uniformity data can be utilized to adjust the volume of developer applied at the first and the second position. The thickness uniformity data can also be used to adjust the flow rate of the developer applied at each nozzle tip of the multiple tip nozzle. In another aspect of the invention, the thickness uniformity data can be used to adjust the offset position of the first and the second position with respect to the same central axis. The systems can be combined to provided for an adjustment of any of the offset positions, the volume of developer applied and the flow rate of the developer at each nozzle tip onto the photoresist material layer.
One particular aspect of the invention relates to a system for applying a developer material onto a photoresist material layer disposed on a substrate to provide a uniformly thick layer of developer material. The layer of developer material is spincoated onto the substrate by a rotating chuck coupled to a motor. The system includes a nozzle adapted to apply a predetermined volume of developer on a photoresist material layer along a linear path having a length approximately equal to the diameter of the substrate and a movement system adapted to move the nozzle to a first position offset from a central region of the photoresist material for applying a first predetermined volume of developer onto the photoresist material while it is spin coated and adapted to move the nozzle to a second position offset from the central region for applying a second predetermined volume of developer onto the photoresist material while it is spin coated. The first position is located on an opposite side of the central region with respect to the second position.
Another aspect of the present invention relates to a system for applying a developer material onto a photoresist material layer disposed on a substrate to provide a uniformly thick layer of developer material. The layer of developer material is spincoated onto the substrate by a rotating chuck coupled to a motor. The system includes a nozzle adapted to apply a predetermined volume of developer on a photoresist material layer along a linear path having a length approximately equal to the diameter of the substrate and a movement system adapted to move the nozzle to a first position offset from a central region of the photoresist material for applying a first predetermined volume of developer to the photoresist material while it is spin coated and adapted to move the nozzle to a second position offset from the central region for applying a second predetermined volume of developer to the photoresist material while it is spin coated. The first position is located on an opposite side of the central region with respect to the second position. The system also includes a measuring system adapted to measure the thickness of the layer of photoresist material that has been developed by the developer material and a processor operatively coupled to the measuring system and a volume control system. The processor receives thickness data from the measuring system and the processor using the data to provide adjustment information to the volume control system for adjusting the volume of developer applied to at least one of the first position and the second position, so that a layer of developed photoresist material having a more uniform thickness can be achieved for a subsequent substrate.
Another aspect of the present invention relates to a system for applying a developer material onto a photoresist material layer disposed on a substrate to provide a uniformly thick layer of developer material. The layer of developer material is spincoated onto the substrate by a rotating chuck coupled to a motor. The system includes a nozzle adapted to apply a predetermined volume of developer on a photoresist material layer along a linear path having a length approximately equal to the diameter of the substrate and a movement system adapted to move the nozzle to a first position offset from a central region of the photoresist material for applying a first predetermined volume of developer to the photoresist material while it is spin coated and adapted to move the nozzle to a second position offset from the central region for applying a second predetermined volume of developer to the photoresist material while it is spin coated. The first position is located on an opposite side of the central region with respect to the second position. The system also includes a measuring system adapted to measure the thickness of the layer of photoresist material that has been developed by the developer material and a processor operatively coupled to the measuring system and an offset movement system. The processor receives thickness data from the measuring system and the processor using the data to provide adjustment information to the offset movement system for adjusting the offset location of at least one of the first position and the second position, so that a layer of developed photoresist material having a more uniform thickness can be achieved for a subsequent substrate.
Yet another aspect of the present invention relates to a system for applying a developer material onto a photoresist material layer disposed on a substrate to provide a uniformly thick layer of developer material. The layer of developer material is spincoated onto the substrate by a rotating chuck coupled to a motor. The system includes means for applying a predetermined volume of developer on a photoresist material layer along a linear path having a length approximately equal to the diameter of the substrate and means for moving the nozzle to a first position offset from a central region of the photoresist material for applying a first predetermined volume of developer to the photoresist material while it is spin coated and a second position offset from the central region for applying a second predetermined volume of developer to the photoresist material while it is spin coated, the first position being located on an opposite side of the central region with respect to the second position.
Still yet another aspect of the present invention relates to a method for applying a developer with a multiple tip nozzle onto a photoresist material layer disposed on a substrate to provide a uniformly thick layer of developer material. The layer of developer material is spincoated onto the substrate by a rotating chuck coupled to a motor. The method includes the steps of spinning the photoresist material layer at a predetermined speed, moving the nozzle to a first position offset from a central region of the photoresist material layer and applying a first position predetermined volume of developer, moving the nozzle to a second position offset from a central region of the photoresist material layer on an oppose side of the central region with respect to the first position and applying a second position predetermined volume of developer, spin coating the substrate until the developer forms a layer on the photoresist material, stopping the spinning of the substrate until the developer develops the photoresist material, measuring the thickness of the developed photoresist material layer at a variety of areas on the photoresist material layer and generating data based on the measurements, determining the thickness uniformity of the layer based on the data and adjusting one of the first position, second position, the first position predetermined volume and the second position predetermined volume.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.